The braking systems in most modern aircraft comprise brakes having disks of steel or carbon stacked around a torsion tube, together with braking actuators carried by a ring and controlled to apply a braking force against the disks in order to exert a braking torque on the braked wheels of the aircraft, tending to slow the aircraft down. Generally, the braked wheels are the wheels of the main landing gear of the aircraft.
A distinction is drawn between hydraulic brakes, in which the actuators are fed with a pressurized fluid and include a piston, and electromechanical brakes, in which the actuators are powered electrically and include an electric motor adapted to move a pusher.
The time required for brake disks to cool down is a parameter that is crucial for defining the turnaround time (TAT) of an aircraft. The TAT is the minimum time to be allowed between two flights of an aircraft, i.e. the time during which the aircraft must remain on the ground after landing and before takeoff. In addition to cooling the brake disks, numerous parameters are involved in defining the TAT, including the time required for allowing passengers to leave the aircraft and to enter it, the time required to fill its tanks with fuel, the time required for maintenance operations, etc.
Before takeoff, it is important for the temperature of the stack of disks to be less than a safe maximum temperature above which braking performance is degraded (in the event of emergency braking during takeoff), and above which there is a real danger of fire once the landing gear enters into the wheel bays in the retracted position, in particular in the event of hydraulic fluid being projected onto the brake disks.
In order to measure the temperature of the stack of disks, it is known to make use of a temperature sensor installed in a cavity of the torsion tube of the brake. The sensor is then heated by radiation and by conduction via the tube, which is detrimental to the representative nature of the measurement.
This measurement uncertainty makes it necessary to take a certain margin into account between the temperature delivered by the sensor and the safe maximum temperature.
This margin has the effect of increasing the time required for cooling the brakes, and thus of increasing the TAT.